An automatic variable transmission or continuously variable transmission for vehicles (such as motorcycles) is commercially available in a weight roller structure of automatic variable transmission device which comprises a movable transmission disc formed with a plurality of weight roller rooms. Each weight roller room is provided with a weight roller. Each weight roller is subject to a holding disc. Through the centrifugal outward displacement of the weight rollers, the movable transmission disc is forced to move toward a drive disc along a central shaft so that the distance between the movable transmission disc and the drive disc is reduced and changed and a V-shaped transmission belt between the movable transmission disc and the drive disc can change its transmission position with the speed of the movable transmission disc to achieve the effect of an automatic speed change.
For the aforesaid conventional automatic variable transmission or continuously variable transmission to achieve the object of a stepless automatic speed change, as shown in FIGS. 1, 2, 3 and 4, the center of a movable transmission disc 1 is radially formed with a plurality of weight roller rooms 11 each having a push surface 110 inclined inward. Each weight roller room 11 is provided with a weight roller 3. Each weight roller 3 on the push surface 110 is subject to an inclined disc body portion 20 of a holding disc 2. As shown in FIG. 5 and FIG. 6, when the drive disc 5 is driven by a central shaft 6, the movable transmission disc 1 is forced to move toward the drive disc 5 along the central shaft 6 through the centrifugal outward displacement of the weight rollers 3, so that the distance between the movable transmission disc 1 and the drive disc 5 is reduced and changed, and a V-shaped transmission belt 4 between the movable transmission disc 1 and the drive disc 5 can change its transmission position from inside to outside with the rotational speed of the movable transmission disc 1 to change the transmission speed ratio of the V-shaped transmission belt 4. As shown in FIG. 3 and FIG. 6, through the centrifugal outward displacement of the weight rollers 3, the movable transmission disc 1 is forced to move axially to change the distance between the movable transmission disc 1 and the drive disc 5 and further to change the transmission position of the V-shaped transmission belt 4. When the center shaft 6 drives the drive disc 5 and the holding disc 2, in order to prevent the weight rollers 3 from being displaced from the inclined disc body portion 20 of the holding disc 2, as shown in FIG. 1, FIG. 2 and FIG. 4, the movable transmission disc 1 is provided with a plurality of guide posts 12 extending outward and each disposed between every two of the weight roller rooms 11. In addition, the inclined disc body portion 20 of the holding disc 2 is formed with a plurality of recesses 200. The recesses 200 are formed with guide notches 21 corresponding to the guide posts 12. Through the guide posts 12 engaged in the guide notches 21 respectively, the holding disc 2 is synchronously rotated with the movable transmission disc 1, thereby preventing the press surface that the inclined disc body portion 20 of the holding disc 2 acts on the weight rollers 3 from being deviated. The holding disc 2 is not allowed to be axially displaced because the notches 21 are mated with the guide posts 12 of the movable transmission disc 1 to form a synchronous link. As a result, during the axial displacement of the movable transmission disc 1, a strong frictional resistance is formed between the guide posts 12 and the guide notches 21 to lower the flexibility of changing the distance between the movable transmission disc 1 and the drive disc 5. This affects the smoothness of the V-shaped transmission belt 4 to change its transmission position or affects the efficiency of a speed change. Accordingly, the inventor of the present invention has devoted himself based on his many years of practical experiences to solve these problems.